Image filter processing apparatus and method

ABSTRACT

A memory stores an output value as a filter processing result. A first calculator calculates a difference between an input value of an image signal and the output value stored in the memory. The output value is the filter processing result of a previous input value. A lookup table stores a plurality of difference values and change values, and outputs the change value corresponding to the difference calculated by the first calculator. The change value is a product of the difference and a value which is above “0” and below “1” if an absolute value of the difference is below a threshold, and the change value is a product of the difference and a value which is above “−1” and below “0” if the absolute value is above the threshold. A second calculator outputs a difference between the input value and the change value.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application PH2000-280832, filed on Sep.14, 2000; the entire contents of which are incorporated herein byreference.

FIELD OF THE INVENTION

[0002] The present invention relates to an image filter processingapparatus and method for effectively executing a post filter processingfor an image.

BACKGROUND OF THE INVENTION

[0003] Post filter processing is a filter processing for an image aftersome processing is executed for the image. For example, after a dynamicimage is decoded, post filter processing reduces noise caused bycompression in case of coding the dynamic image. Especially, in imagecoding methods using DCT (Discrete Cosine Transformation) such as MPEGmethod, block noise is generated because of coding by unit of block, andmosquito noise as quasi-high frequency element is generated because ofquantization. Furthermore, a high frequency element is lost byquantization in case of coding. As a result, an edge part in an imagebecomes dull and the image blurs.

[0004] In order to improve these defects, in general, the post filterprocessing is adaptively executed based on characteristics of the image.However, in typical post filter processing, the filter processing isexecuted pixel-by-pixel on the image, and a large calculation quantityis necessary. For example, in case of CIF format used for “ITU-TH.261,H.263, ISO/IEC MPEG-4”, as for luminance signal on the image, “352”pixels along a horizontal line and “288” pixels along a vertical lineare included, and the filter processing must be executed for a total of“101, 376” pixels. If such processing of large calculation quantity isperformed by software, the real time processing becomes difficult. If itis performed by hardware, the cost becomes expensive.

[0005] On the other hand, in case of size conversion of coded image, asize conversion method using a filter after decoding and a sizeconversion method using conversion coefficients such as DCT coefficient,are well known. In both methods, if the size of an image including acoded noise is converted, the coded noise is also expanded by the sizeconversion processing. Accordingly, even if the post filter processingis executed after size conversion, the coded noise remains in the image.Furthermore, if the size conversion processing is executed after thepost filter processing, in case of magnification, the image becomesblurred. In case of reduction, an aliasing is generated, by sharpeningprocessing.

[0006] As mentioned-above, in the post filter processing of the priorart, the filter processing is executed pixel-by-pixel on the image.Accordingly, a large calculation quantity is necessary. Furthermore, inthe size conversion processing of the image, in case of size conversionof coded image, the post filter processing cannot be effectivelyexecuted for the encoded image.

BRIEF SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide an imagefilter processing apparatus and method for simultaneously executing anoise reduction filter processing and a sharpening filter processing forthe image by small calculation quantity.

[0008] According to an aspect of the present invention, there isprovided an image filter processing apparatus, comprising: a memoryconfigured to temporarily store an output value as a filter processingresult; a first calculator configured to calculate a difference betweenan input value of image signal and the output value stored in saidmemory, the output value being the filter processing result of aprevious input value by one unit time; a lookup table configured torespectively store a plurality of difference values and a change value,and to output the change value corresponding to the differencecalculated by said first calculator, the change value being a product ofthe difference and a value which is above “0” and below “1” if anabsolute value of the difference is below a threshold, and the changevalue being a product of the difference and a value which is above “−1”and below “0” if the absolute value is above the threshold; and a secondcalculator configured to output a difference between the input value andthe change value, an output value as the difference being newly storedin said memory.

[0009] Further in accordance with another aspect of the presentinvention, there is also provided an image filter processing method,comprising: temporarily storing an output value as a filter processingresult in a memory; calculating a difference between an input value ofimage signal and the output value stored in the memory, the output valuebeing the filter processing result of a previous input value by one unittime; outputting a change value corresponding to the difference, thechange value being a product of the difference and a value which isabove “0” and below “1” if an absolute value of the difference is belowa threshold, and the change value being a product of the difference anda value which is above “−1” and below “0” if the absolute value is abovethe threshold; and outputting a difference between the input value andthe change value, the output value as the difference being newly storedin the memory.

[0010] Further in accordance with another aspect of the presentinvention, there is also provided an image processing apparatus, a noisereduction filter processing unit configured to execute a noise reductionfilter processing for input image signal; a size conversion processingunit configured to execute a size conversion processing for image signaloutput from said noise reduction filter processing unit; and asharpening filter processing unit configured to execute a sharpeningfilter processing for image signal output from said size conversionprocessing unit; wherein said noise reduction filter processing unitincluding: a memory configured to temporarily store an output value asthe noise reduction filter processing result; a first calculatorconfigured to calculate a difference between an input value of the imagesignal and the output value stored in said memory, the output valuebeing the noise reduction filter processing result of a previous inputvalue by one unit time; a lookup table configured to respectively storea plurality of difference values and a change value, and to output thechange value corresponding to the difference calculated by said firstcalculator, the change value being a product of the difference and avalue which is above “0” and below “1” if an absolute value of thedifference is below a threshold; and a second calculator configured tooutput a difference between the input value and the change value, anoutput value as the difference being newly stored in said memory;wherein said sharpening filter processing unit including: a memoryconfigured to temporarily store an output value as a sharpening filterprocessing result; a first calculator configured to calculate adifference between an input value of image signal and the output valuestored in said memory, the output value being the sharpening filterprocessing result of a previous input value by one unit time; a lookuptable configured to respectively store a plurality of difference valuesand a change value, and to output the change value corresponding to thedifference calculated by said first calculator, the change value being aproduct of the difference and a value which is above “−1” and below “0”if an absolute value of the difference is above a threshold; and asecond calculator configured to output a difference between the inputvalue and the change value, an output value as the difference beingnewly stored in said memory.

[0011] Further in accordance with another aspect of the presentinvention, there is also provided an image processing method,comprising: executing a noise reduction filter processing for inputimage signal; executing a size conversion processing for image signal ofthe noise reduction processing result; and executing a sharpening filterprocessing for image signal of the size conversion processing result; atthe executing step of the noise reduction filter processing, comprising:temporarily storing an output value as the noise reduction filterprocessing result in a memory; calculating a difference between an inputvalue of the image signal and the output value stored in the memory, theoutput value being the noise reduction filter processing result of aprevious input value by one unit time; outputting a change valuecorresponding to the difference, the change value being a product of thedifference and a value which is above “0” and below “1” if an absolutevalue of the difference is below a threshold; and outputting adifference between the input value and the change value, an output valueas the difference being newly stored in the memory; at the executingstep of the sharpening filter processing, comprising: temporarilystoring an output value as a sharpening filter processing result in amemory; calculating a difference between an input value of image signaland the output value stored in the memory, the output value being thesharpening filter processing result of a previous input value by oneunit time; outputting a change value corresponding to the difference,the change value being a product of the difference and a value which isabove “−1” and below “0” if an absolute value of the difference is abovea threshold; and outputting a difference between the input value and thechange value, an output value as the difference being newly stored inthe memory.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a block diagram of the image filter processing apparatusaccording to a first embodiment of the present invention.

[0013]FIG. 2 is a schematic diagram showing a concept of a lookup table.

[0014]FIG. 3 is a schematic diagram of an example of contents of thelookup table according to the first embodiment of the present invention.

[0015]FIG. 4 is a flow chart of a post filter processing according tothe first embodiment of the present invention.

[0016]FIGS. 5A, 5B, 5C and 5D are examples showing a scan direction toinput the image data.

[0017]FIG. 6 is a schematic diagram showing an effect of the post filterprocessing according to the first embodiment of the present invention.

[0018]FIG. 7 is a flow chart of an image filter processing according toa second embodiment of the present invention.

[0019]FIG. 8 is a block diagram of the image processing apparatusaccording to the second embodiment of the present invention.

[0020]FIG. 9 is a schematic diagram of concrete of contents of thelookup table in a noise reduction filter processing unit according tothe second embodiment of the present invention.

[0021]FIG. 10 is a schematic diagram of example of contents of thelookup table in a sharpening filter processing unit according to thesecond embodiment of the present invention.

[0022]FIG. 11 is a schematic diagram showing an effect of the imagefilter processing according to the second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, various embodiments of the present invention will beexplained by referring to the drawings. FIG. 1 is a block diagram of theimage filter processing apparatus according to the first embodiment ofthe present invention. The image filter processing apparatus includes:an input terminal 100 to input a pixel value (input value) of an imagesignal, an output terminal 105 to output a pixel value (output value aspost filter processing result) of a previous image signal advanced byone time unit compared with the input image signal, an adder 101 tocalculate a difference between the input value and the output value, alookup table to output a change value corresponding to the difference asan address, an adder 103 to calculate an output value by changing theinput value based on the change value, and a memory 104 to temporarilystore the output value. In the lookup table 102, each of a plurality ofdifferences calculated by the adder 101 and corresponding change valuesare previously stored.

[0024] Next, operation of the image filter processing apparatus of thefirst embodiment is explained. Assume that the input value is P[t] andthe output value is Q[t]. In this case, “t” represents the position of apixel. In order to execute the filter processing for the pixel ofposition “t”, the input value P[t] and the output value Q[t−1] of aprevious pixel of position “t−1” stored in the memory 104, are input tothe adder 101. The adder 101 calculates a difference “d” between theinput value P[t] and the output value Q[t−1]. The lookup table 102receives the difference “d”, and a change value “f(d)” is output fromthe lookup table 102 to the adder 103. The adder 103 subtracts thechange value f(d) from the input value P[t] and generates the outputvalue Q[t] as the difference. A series of this operation is representedby the following expressions.

Q[t]=P[t]−f(d)  (1)

d=P[t]−Q[t−1]  (2)

[0025] In the lookup table 102, a large number of change values “f(d)”previously calculated by function “f” are stored in correspondence witheach difference “d”. For example, if the pixel value is eight bit datawhose limit is “0˜255”, a limit of the difference “d” is “−255˜+255”. Inthis case, the lookup table 102 prepares 511 units of arrangement.Accordingly, in this image filter processing apparatus, calculationnecessary for filter processing of one pixel is two times addition bythe adders 101 and 103.

[0026] As shown in the following expression (3), the basis of thisfilter processing is a weighted sum of the input pixel value P[t] as apresent pixel and the output value Q[t−1] corresponding to an inputpixel value P[t−1] as a previous pixel neighboring the present pixel. Inthis case, a weighted coefficient “α” changes with the difference “d”.

Q[t]=(1−α)P[t]+αQ[t−1]  (3)

[0027] The calculation of the weighted coefficient “α” is represented bythe difference “d” in the expression (2) as a variable as follows.

Q[t]=P[t]−αd  (4)

[0028] Where:

0<α<1  (5)

[0029] Q[t] is a weighted average of the input value P[t] of the presentpixel and the output value Q[t−1] of the previous pixel. Thiscalculation represents a smoothing processing.

[0030] On the other hand, if:

−1<α<0  (6)

[0031] Q[t] is calculated by adding a change value to P[t], and thechange value is determined in proportion to the difference between theinput value P[t] and the output value Q[t−1]. This calculationrepresents a sharpening processing. FIG. 2 shows a graph representingthe above-mentioned relation. In this graph, the vertical axisrepresents “f(d)” and the horizontal axis represents “d”. In FIG. 2, anarea represented by oblique lines of right ascent corresponds to theexpression (5), and an area represented by oblique lines of right dropcorresponds to the expression (6).

[0032]FIG. 3 shows an example of contents of the lookup table. As shownin FIG. 3, if an absolute value of the difference “d” is below athreshold “dth”, the change value “f(d)” corresponds to the area of theexpression (5). If the absolute value of the difference “d” is above thethreshold “dth”, the change value “f(d)” corresponds to the area of theexpression (6). By setting such change value “f(d)”, as for minutechange of pixel value for two neighboring pixels, the coded noise isreduced by the smoothing process. Furthermore, as for a large change ofpixel value for two neighboring pixels, the present pixel is decided tobe an edge part and emphasized as the edge by the sharpening process.

[0033] In this filter processing, the previous output value Q[t−1] byone unit of time compared with the input value P[t], i.e., the outputvalue Q[t−1] of previous pixel “t−1” neighboring the present pixel “t”of the input value P[t], is utilized. In this cyclic filter processing,a phase-lag is generated, and it is not suitable for this processing tosimply utilize for image processing. Accordingly, hereinafter, byexecuting this processing a plurality of times, this problem is avoided.

[0034]FIG. 4 is a flow chart of the post filter processing using theimage filter processing apparatus in FIG. 1. In this post filterprocessing, the filter processing is executed along four directions ofthe frame for the input image. First, a post filter processing isexecuted along a scan direction from right to left on the frame (S101).As shown in FIG. 5A, the post filter processing is executed for eachpixel along a scan direction from right to left in order. Next, the postfilter processing is executed along a reverse scan direction from leftto right on the frame (S102). As shown in FIG. 5B, the post filterprocessing is executed for each pixel along a scan direction from leftto right in order. In the same way, the post filter processing isexecuted along a scan direction from the upper part to the lower part(S103). Next, the post filter processing is executed along a scandirection from the lower part to the upper part (S104). As shown inFIGS. 5C and 5D, the post filter processing is executed for each pixelalong a scan direction from the upper part to the lower part and along areverse scan direction from the lower part to the upper part in order.

[0035] If the input signal is a color image signal, for example, aluminance signal Y and two chrominance signals Cb and Cr, theabove-mentioned post filter processing is respectively executed forthree signals Y, Cb, Cr of each pixel. In this way, by executing filterprocessing along mutual reverse directions, the phase-lag as a defect ofthe cyclic filter processing using previous output value is avoided.Furthermore, even if the filter processing is executed along fourdirections as shown in FIGS. 5A˜5D, the calculation quantity necessaryfor the filter processing of one pixel is eight times addition only.

[0036] In the first embodiment, the filter processing is executed inorder along each direction from right to left, from left to right, fromupper part to lower part, and from lower part to upper part. However, ifthe first direction and the second direction respectively includes aseffect to mutually reduce a noise, the order of the directions may bearbitrarily determined. Furthermore, four directions are shown asexample in FIGS. 5A˜5D. However, two directions between right and left,or between upper part and lower part, may be used. Alternatively, eightdirections including slant directions may be used.

[0037]FIG. 6 shows a schematic diagram of effect of the post filterprocessing according to the first embodiment. As a specific feature ofthis filter processing, a signal element with a small change such ascoded noise is reduced by a smoothing process. Conversely, a signalelement with a large change such as an edge is emphasized by asharpening process. In this way, by executing the post filterprocessing, an image in which a noise feeling is few and a sharp degreeis high is obtained.

[0038] As mentioned-above, in the image filter apparatus of the firstembodiment, the reduction of coded noise and the sharpening of edge canbe simultaneously executed by small calculation quantity.

[0039] Next, as the second embodiment of the present invention, anexample to execute the post filter processing and a size conversionprocessing for coded image is explained. FIG. 7 is a flow chart ofprocessing in case of executing both the post filter processing and thesize conversion processing for the coded image. FIG. 8 is a blockdiagram of the image processing apparatus according to the secondembodiment.

[0040] First, a noise reduction filter processing unit 201 executes apost filter processing of noise reduction (S201). The noise reductionfilter processing unit 201 includes the same components of the imagefilter processing apparatus as in the first embodiment. As shown in FIG.8, the noise reduction filter processing unit 201 includes an adder101A, a lookup table 102A, an adder 103A, and a memory 104A. In thiscase, a function “f(d)” used for the lookup table 102A is shown in FIG.9. If an absolute value of the difference “d” is below a threshold value“dth”, the function “f(d)” is represented as values corresponding toarea of the expression (5).

[0041] Next, as for the image of which noise is reduced at S201, a sizeconversion processing unit 202 composed of a typical FIR filter executesa conversion processing of image size (S202). As one example, a methodfor utilizing FIR filter of five taps used for SM3 as test model ofMPEG-1 is explained. In this method, in case of double-magnification ofimage size, zero-interpolation is executed for space between pixelsalong the magnification direction on the image, and a magnified image iscreated using FIR filter of five taps “(−3, 0, 35, 64, 35, 0, −3)/128”.In case of half-reduction of image size, pixels of the image aresub-sampled at ½ rate using FIR filter of five taps “(−29, 0, 88, 138,88, 0, −29)/256”.

[0042] A sharpening filter processing unit 203 executes a post filterprocessing of sharpening (S203). The sharpening filter processing unit203 includes the same components as the image filter processingapparatus in the first embodiment. As shown in FIG. 8, the sharpeningfilter processing unit 203 includes an adder 101B, a lookup table 102B,an adder 103B, and a memory 104B. In this case, a function “f(d)” usedfor the lookup table 102B is shown in FIG. 10. If an absolute value ofthe difference “d” is above a threshold “dth”, the function “f(d)” isrepresented as values corresponding to area of the expression (6).Accordingly, if a difference between two pixel values of a present pixeland a previous pixel is above the threshold, the present pixel isdecided as an edge part and emphasized as the edge part by using thesharpening process.

[0043]FIG. 11 shows an effect of the image filter processing of thesecond embodiment in case of executing the noise reduction filterprocessing, the size conversion processing (magnification processing),and the sharpening filter processing. First, a minute change element ofcoded noise is removed by the noise reduction filter. Next, the imagehaving the coded noise removed is magnified. Then, an edge part in themagnified image is emphasized by the sharpening filter. By executingeach processing in this order, in case of magnification, the magnifiedimage does not include the coded noise but includes sharp edges.

[0044] As mentioned-above, in the present invention, the coded noisereduction processing and the sharpening processing can be simultaneouslyexecuted by few calculation quantity. Furthermore, in case of executingthe size conversion processing, the post filter processing can beeffectively executed for the coded image.

[0045] A memory can be used to store instructions for performing theprocess described above, such a memory can be a CD-ROM, floppy disk,hard disk, magnetic tape, semiconductor memory, and so on.

[0046] Other embodiments of the invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with the true scope andspirit of the invention being indicated by the following claims.

What is claimed is:
 1. An image filter processing apparatus, comprising:a memory configured to temporarily store an output value as a filterprocessing result; a first calculator configured to calculate adifference between an input value of an image signal and the outputvalue stored in said memory, the output value being the filterprocessing result of a previous input value; a lookup table configuredto respectively store a plurality of differences and correspondingchange values, and to output a change value corresponding to thedifference calculated by said first calculator, the change value being aproduct of the difference and a value which is above “0” and below “1”if an absolute value of the difference is below a threshold, and thechange value being a product of the difference and a value which isabove “−1” and below “0” if the absolute value is above the threshold;and a second calculator configured to output a difference between theinput value and the change value and to store the difference being newlystored in said memory.
 2. The image filter processing apparatusaccording to claim 1, wherein the input value corresponds to one pixelof an image, and wherein the previous input value corresponds to anotherpixel neighboring the one pixel along the same scan line on the image.3. The image filter processing apparatus according to claim 2, whereinthe input value includes at least a luminance signal of the one pixel.4. The image filter processing apparatus according to claim 3, furthercomprising an input terminal configured to continually input the imagepixel-by-pixel along a scan direction.
 5. The image filter processingapparatus according to claim 4, where in said input terminal inputs theimage along one of the scan directions from right to left and from leftto right, and inputs the image again along the other of the scandirections.
 6. The image filter processing apparatus according to claim4, wherein said input terminal inputs the image along one of the scandirections from upper part to lower part and from lower part to upperpart, and inputs the image again along the other of the scan directions.7. The image filter processing apparatus according to claim 2, whereinsaid memory temporarily stores the output value of the pixel neighboringthe one pixel while said input terminal inputs the image signal of theone pixel.
 8. The image filter processing apparatus according to claim7, wherein said first calculator subtracts the output value of theneighboring pixel from the input value of the one pixel, the subtractionresult being the difference.
 9. The image filter processing apparatusaccording to claim 8, wherein said second calculator subtracts thechange value from the input value of the one pixel, the subtractionresult being the output value of the one pixel.
 10. An image filterprocessing method, comprising: temporarily storing an output value as afilter processing result in a memory; calculating a difference betweenan input value of an image signal and the output value stored in thememory, the output value being the filter processing result of aprevious input value; outputting a change value corresponding to thedifference, the change value being a product of the difference and avalue which is above “0” and below “1” if an absolute value of thedifference is below a threshold, and the change value being a product ofthe difference and a value which is above “−1” and below “0” if theabsolute value is above the threshold; outputting a difference betweenthe input value and the change value; and storing the difference in thememory.
 11. A computer program product for use with a computer,comprising: a computer usable medium having computer readable programcode embodied in said medium for causing said computer to execute filterprocessing for an image, said computer readable program code having:computer readable program code to temporarily store an output value as afilter processing result in a memory; computer readable program code tocalculate a difference between an input value of an image signal and theoutput value stored in the memory, the output value being the filterprocessing result of a previous input value; computer readable programcode to output a change value corresponding to the difference, thechange value being a product of the difference and a value which isabove “0” and below “1” if an absolute value of the difference is belowa threshold, and the change value being a product of the difference anda value which is above “−1” and below “0” if the absolute value is abovethe threshold; and computer readable program code to output a differencebetween the input value and the change value, and to store thedifference in the memory.
 12. An image processing apparatus, comprising:a noise reduction filter processing unit configured to execute a noisereduction filter processing of an input image signal; a size conversionprocessing unit configured to execute a size conversion processing of animage signal output from said noise reduction filter processing unit;and a sharpening filter processing unit configured to execute asharpening filter processing of an image signal output from said sizeconversion processing unit; wherein said noise reduction filterprocessing unit including: a first memory configured to temporarilystore an output value as a noise reduction filter processing result; afirst calculator configured to calculate a difference between an inputvalue of the image signal and the output value stored in said firstmemory, the output value stored in said first memory being the noisereduction filter processing result of a previous input value of theimage signal; a first lookup table configured to store a plurality ofdifferences and corresponding change values, and to output a changevalue corresponding to the difference calculated by said firstcalculator, the change value being a product of the difference and avalue which is above “0” and below “1” if an absolute value of thedifference is below a threshold; and a second calculator configured tooutput a difference between the input value and the change value fromthe first lookup table and to store the difference in said first memory;wherein said sharpening filter processing unit including: a secondmemory configured to temporarily store an output value as a sharpeningfilter processing result; a third calculator configured to calculate adifference between an input value from said size conversion processingunit and the output value stored in said second memory, the output valuestored in said second memory being the sharpening filter processingresult of a previous input value from said size conversion processingunit; a second lookup table configured to store a plurality ofdifferences and corresponding change values, and to output the changevalue corresponding to the difference calculated by said thirdcalculator, the change value being a product of the difference and avalue which is above “−1” and below “0” if an absolute value of thedifference is above a threshold; and a fourth calculator configured tooutput a difference between the input value from said size conversionprocessing unit and the change value from the second lookup table, andto store the difference in said second memory.
 13. The image processingapparatus according to claim 12, wherein the input value of the imagecorresponds to one pixel of an image, and wherein the previous inputvalue of the image signal corresponds to a pixel neighboring the onepixel along the same scan line on the image.
 14. The image processingapparatus according to claim 13, wherein the input value of the imagesignal includes at least a luminance signal of the one pixel.
 15. Theimage processing apparatus according to claim 14, wherein said noisereduction filter processing unit further comprising an input terminalconfigured to continually input the image pixel-by-pixel along a scandirection.
 16. The image processing apparatus according to claim 15,wherein said input terminal inputs the image along one of the scandirections from right to left and from left to right, and inputs theimage again along the other of the scan directions.
 17. The imageprocessing apparatus according to claim 15, wherein said input terminalinputs the image along one of the scan directions from upper part tolower part and from lower part to upper part, and inputs the image againalong the other of the scan directions.
 18. The image processingapparatus according to claim 12, wherein said size conversion processingunit executes a magnification processing for the image signal outputfrom said noise reduction filter processing unit.
 19. The imageprocessing apparatus according to claim 15, in said noise reductionfilter processing unit, wherein said first calculator subtracts theoutput value of the previous pixel from the input value of the onepixel, the output value of the previous pixel being obtained from saidfirst memory, the input value of the one pixel being obtained from saidinput terminal, and wherein said second calculator subtracts the changevalue from the input value of the one pixel, the subtraction resultbeing input as a noise reduction filter processing result of the onepixel to said size conversion processing unit.
 20. The image processingapparatus according to claim 19, in said sharpening filter processingunit, wherein said third calculator subtracts the output value of theprevious pixel from the input value of the one pixel, the output valueof the previous pixel being obtained from said second memory, the inputvalue of the one pixel being obtained from said size conversionprocessing unit, and wherein said fourth calculator subtracts the changevalue from the input value of the one pixel, the subtraction resultbeing output as a sharpening filter processing result of the one pixel.21. An image processing method, comprising: executing a noise reductionfilter processing for an input image signal; executing a size conversionprocessing of an image signal of the noise reduction processing result;and executing a sharpening filter processing of an image signal of thesize conversion processing result; the executing step of the noisereduction filter processing, comprising: temporarily storing an outputvalue as the noise reduction filter processing result in a first memory;calculating a difference between an input value of the image signal andthe output value stored in the first memory, the output value stored inthe first memory being the noise reduction filter processing result of aprevious input value of the image signal; outputting a first changevalue corresponding to the difference between the input value of theimage signal and the output value stored in the first memory, the firstchange value being a product of the difference and a value which isabove “0” and below “1” if an absolute value of the difference is belowa threshold; and outputting a difference between the input value of theimage signal and the first change value; and storing the differencebeing newly stored in the first memory; the executing step of thesharpening filter processing, comprising: temporarily storing an outputvalue as a sharpening filter processing result in a second memory;calculating a difference between an input value from the size conversionprocessing and the output value stored in the second memory, the outputvalue stored in the second memory being the sharpening filter processingresult of a previous input value; outputting a second change valuecorresponding to the difference between an input value from the sizeconversion processing and the output value stored in the second memory,the second change value being a product of the difference and a valuewhich is above “−1” and below “0” if an absolute value of the differenceis above a threshold; and outputting a difference between the inputvalue from the size conversion processing and the second change value;and storing the difference in the second memory.
 22. A computer programproduct for use with a computer, comprising: a computer usable mediumhaving computer readable program code embodied in said medium forcausing said computer to execute image processing, said computerreadable program code having: computer readable program code to executea noise reduction filter processing of an input image signal; computerreadable program code to execute a size conversion processing of animage signal of the noise reduction processing result; and computerreadable program code to execute a sharpening filter processing of animage signal of the size conversion processing result; said program codeto execute the noise reduction filter processing, comprising: computerreadable program code to temporarily store an output value as the noisereduction filter processing result in a first memory; computer readableprogram code to calculate a difference between an input value of theimage signal and the output value stored in the first memory, the outputvalue stored in the first memory being the noise reduction filterprocessing result of a previous input value; computer readable programcode to output a first change value corresponding to the differencebetween the input value of the image signal and the output value storedin the first memory, the first change value being a product of thedifference and a value which is above “0” and below “1” if an absolutevalue of the difference is below a threshold; and computer readableprogram code to output a difference between the input value of the imagesignal and the first change value, and to store the difference in thefirst memory; said program code to execute the sharpening filterprocessing, comprising: computer readable program code to temporarilystore an output value as a sharpening filter processing result in asecond memory; computer readable program code to calculate a differencebetween an input value from the size conversion processing program codeand the output value stored in the second memory, the output valuestored in the second memory being the sharpening filter processingresult of a previous input value; computer readable program code tooutput a second change value corresponding to the difference between theinput value from the size conversion processing program code and theoutput value stored in the second memory, the second change value beinga product of the difference and a value which is above “−1” and below“0” if an absolute value of the difference is above a threshold; andcomputer readable program code to output a difference between the inputvalue from the size conversion processing program code and the secondchange value, and to store the difference in the second memory.